Surfactants



Edited rates i atent: @hfice 356749348 Patented Feb. 26, 1953 Thisinvention relates to improvements in the art of cleaning objects,particularly those made of metal, glass, etc.

Broadly stated, the invention pertains to alkaline cleaning and, moreparticularly, to surfactants for use in alkaline metal cleaning baths.

An object of the invention is to improve the cleaning efficiency ofalkaline metal cleaners.

Other objects of the invention will in part be obvious and will in partbe disclosed hereinafter.

Alkaline cleaners are the most widely used means in industry forcleaning metal, glass, certain plastics, etc. They are primarily used toprepare metals such as steel, brass, and copper for plating, painting,enameling, rust proofing, pickling, and other operations. Suchpreparation includes the removal of various types of soil such ascutting oils, grinding, buffing, stamping, and drawing compounds used invarious metal-forming operations, as well as rust preventatives,lubricating greases, and various forms of dirt. The alkaline cleaningsolutions may be used for soaking, spraying, or electrolytic types ofcleanmg. Of these, the soaking or tank cleaning technique is mostimportant because of its widespread use in industry.

In the soaking method of cleaning, the metal article to be cleanedusually is dipped in or slowly transported through a hot alkalinesolution with little or no agitation present. The cleaning solutionsemployed generally are made of materials consisting of between about 88to 99 percent by weight of various alkalies, such as caustic soda,sodium metasilicate, soda ash, trisodium phosphate, and tetrasodiumpyrophosphate, and from about 1 to 12 percent by weight of a surfactant.Previously, the most widely used surfactants for this purpose have beenalkylaryl sulfonates and rosin soaps. Usually, the concentration of thecleaning materials (alkali plus surfactant) in the tank or bath ismaintained between 2 and percent of the cleaning solution.

As oil, grease, and other soils are caused to be separated from the partbeing cleaned in the tank, a scumlike layer collects at the top of thebath. If the surfactant employed is not thoroughly soluble in the hotalkaline solution, it also will tend to accumulate in this surfacelayer. When the accumulation of scum in the surface layer becomes sogreat that it tends to coat the otherwise clean part as it is withdrawnfrom the bath, it becomes necessary to skim the soil and undissolvedsurfactant from the top of the tank. Each time this is done, aconsiderable amount of the surfactant is removed and, of course, thistends to lower the concentration of the effective cleaning agents in thebath to a point where the operation of the bath becomes unsatisfactorymuch sooner than it otherwise would if such losses could be minimized oreliminated. One obvious solution to this problem is to employ onlysurfactants that are soluble in hot alkaline solutions.

There are available polyoxyalkylated tert.-carbinamines which are knownto have a detergent effect on metal surfaces and would appear to haveother requisite characteristics for alkaline cleaning purposes. Thesecompositions, which have been disclosed in copending US. applicationSerial No. 632,648, now US. Patent No.

2,871,266, have a structure which may be generally represented by thefollowing formula:

in which R R and R are alkyl groups Whose total carbon atom contentranges from 7 to 23, and m is an integer of 6 to 101.

The difficulty with compounds of the above-mentioned formulas is thatthey lack the requisite solubility property in hot alkaline solutions,such as, for example, 5 percent sodium hydroxide. It was thought thatthis lack of desired solubility could be overcome by completely (oressentially so) sulfating the compound so as to obtain a product havingthe following formula:

in which the values for R R R and m are the same as indicated above, andX is a monovalent cation such as an alkali metal or hydrogen. However,When a number of these compounds were sulfated, they were found to havea materially decreased cleaning efiiciency notwithstanding the fact thatthe product Was quite soluble in hot alkaline solutions. This effectappeared difiicult to explain or otherwise account for, and so effortswere made to determine the mechanism of this change in cleaningperformance.

in the course of the investigation which ensued, it was discovered thatnot all of the polyoxyalkylated tert.-carbinamines would functionefliciently as metal cleaners after they had been sulfated.Specifically, the sulfated amine-s which proved to be useful were thosehaving the following formula:

R1 R -$-NH(o H,o)ms0 X+ in which R +R +R =11 to 14, m is an integer of 6to 101, and X is a monovalent cation such as an alkali metal orhydrogen.

A further discovery was that, of these sulfated amines which had beendemonstrated to possess utility as metal cleaners, only those having acertain narrow range of ethylene oxide units, namely between 12.5 and17.5, gave metal cleaning results which are substantially as good as theresults obtained with the non-sulfated compositions. At the same time,these compounds containing the indicated narrow range of ethylene oxideunits also had the added advantage of complete solubility in the hotalkaline solution and thereby eliminated the objec tion described above,namely, the excessive losses caused when the surface of the cleaningbaths had to be skimmed to remove the scum-like layer.

The foregoing discovery, which was based on the use of amines that werebelieved to have been completely those otherwise excellent compositions.When less than 75 percent sulfated, the compositions are not compatiblewith strong alkali, such as a 5 percent sodium hydroxide solution. Whenmore than 85 percent sulfated, the cleaning efiiciency of thecompositions is considerably diminished. Thus, it is essential, formaximum performance, that the polyoxyalkylated tert.-carbinamines besulfated between about 75 to 85 percent.

In actual practice, our preferred composition is an alkali metal salt,generally sodium salt, of the tert.-carbinamine ethylene oxide sulfate.Such compounds are completely soluble in 5 percent sodium hydroxide attemperatures of 100 C. They are also soluble in concentrations such as10 percent caustic, although not throughout this entire temperaturerange.

Example 1 describesin detail the alkaline metal cleaning test which wasemployed to establish the utility of the present invention. FollowingExample 1, Table I lists a series of tert.-carbinamine ethylene oxidecompounds which have been sulfated in varying amounts from 0 to 100percent. Also indicated for each of these compounds is the cleaningemciency index as determined by the method described below. In thisseries, the ethylene oxide content has been maintained at 15.0 units,this being the amount present in one of the best of the completelysulfated compositions in accordance with the invention disclosed in ourabove-mentioned copending application. The actual conditions of testwere made more severe than the ones which were employed in our othercase in order to more sharply delineate the differences in cleaningeffectiveness. This was done primarily by using less of the surfactantin the cleaning solution than the concentrations described in theexamples in our other application.

EXAMPLE 1 The following test method was used for evaluating thecomparative efiiciencies of various alkaline metal cleanem. The methodwas adapted from a procedure used throughout the industry and which isdescribed by S. Spring, H. Porman and L. Peale in Method of EvaluatingMetal Cleaners, Ind. & Eng. Chem, Analytical Edition, vol. 18, No. 3,pp. 201-204 (1946). Briefly, the test consists of carefully cleaningthin SAE 1010 steel panels (3 x 3") and uniformly coating them with athin film of brightstock mineral oil, which is drained for one hour at35 C. The coated panel is then rotated'for 5 minutes at 30 rpm. in a1000 ml. beaker of the solution being tested. That solution, which ismaintained at a temperature of 82i2 C. in an oil bath, contains 0.07percent active surfactant and 5 percent of a heavy duty alkaline cleanerconsisting of 30 parts caustic soda, 35 parts sodaash and 30 partssodium metasilicate pentahydrate.

' Following this period of alkaline cleansing, the panel is rinsed in anoverflowing beaker of warm water which is approximately 40 C., allowedto drain in air for 20 seconds, and then subjected to a light spray ofdeionized water for approximately seconds on each side. Any area on thepanel which is still coated with residual oil will exhibit readilyvisible droplets which are termed water breaks. On clean areas, acontinuous water film will be observed. By means of a transparentplastic sheet which is the size of the test panel, and which has beenruled off into 100 squares of uniform dimensions, itis possible todetermine the percentage of surface area which does not show any waterbreaks. This value represents an index of the cleaning efficiency of thealkaline cleaner which has been used. Three such panels are run,readings taken for each side of each panel, and the average of the sixsides is considered to represent the cleaning efficiency index for theparticular cleaner composition being tested. For the particular oil andconcentration of surfactant used, etc., the minimum limitof-acceptability has arbitrarily been set at 70 percent,

Table I t-Alkyl Amine (E O)1s Percent Sulfated Cleaning Efficiency(percent) 50 Insoluble in 5% 62.5 NaOH.

1 NorE.The surfactants employed were sulfated, polyethoxylated t-alkylamines, the amines being a commercially available mixture in the rangest-Cm-1sH2s a1NI'-I2. The surfactants were all in the sodium form and thenumber of ethylene oxide units was 15. Their formulas, therefore, weret-C'i -isl-Tes-arNH(czHrOhsSosNil.

Similar data is obtained with the compounds which are exactly the sameexcept for the ethylene oxide content which is varied from 12.5 to 17.5units. Corresponding data is also obtained with compounds which are thesame except that, instead of using the mixture of amines, the aminewhich is polyethoxylated and sulfated is one in the range Of t=C12H25NHzQ t C15H31NH2.

It is readily apparent from the data in the table that thepolyoxyalkylated t-carbinamines which, priorto sulfation, have excellentmetal cleaning abilities when used incombination with strong alkaliesare: (1) not compatible with strong alkali (and therefore unsatisfactoryproducts) when sulfated below 75 percent, because their incompatibilitywith the alkali causes surface loading and resultant excessive losses ofthe cleaner; (2) satisfactory cleaners (in combination with strongalkali) when sulfated between 75 and 85 percent; and (3) unsatisfactorycleaners (with strong alkali) when sulfated over 85 percent and only arelatively small percentage of the surfactant is employed. A furtherindication of the comparative efiectiveness of the present invention maybe had from the fact that a commercially available alkyl aryl sulfonate,which heretofore had been considered to be among the finest surfactantsknown for alkaline metal cleaning applications, only rated a 13 percentcleaning efficiency index under identical test conditions.

The variousamines described above can be prepared by procedures similarto that disclosed in U.S. application Serial No. 632,648 and may besulfated by any of several well-known methods, using sulfuric acid,sulfur trioxide, chlorosulfonic acid, or other suitable sulfatingagents. In Examples 2 and 3 are described preparations of two amines bya suitable process (the latter being the polyoxyethylene adduct of theamine produced inthe former example). In Examples 4 and 5 are describedtypical preparations of a sulfated amine in accordance with the presentinvention.

EXAMPLE 2 In a suitable reaction vessel, there were combined 500 g.(2.54 mols.) t-dodecylamine, 45.8 g. (2.54 mols.) water and g. methanol.This mixture was heated to 80 C. and 139 g. (3.05 mols.) of ethyleneoxide was added at 8085 C. over a period of 2 to 8 hours. At the end ofthis time, the product was isolated by distillation to remove themethanol and water. The yield, of product (N-(t-dodecyl)ethanol amine)amounted to 618.2 g. and had a neutral equivalent of 246.8. This wasequivalent to N- (t-dodecyl)amine combined with 1.18 rnols. of ethyleneoxide. This neutral equivalent indicated that the product contained asmall amount of the diethanol amine.

5 EXAMPLE 3 In an appropriate reaction vessel, there Were combined 402.3g. N-(t-dodecyDethanol amine (from above), having a neutral equivalentof 246.8, with 989.7 g. ethyleneoxide in the presence of 1.6 g. powderedpotassium hydroxide at 140-180 C. When the reaction was complete, thecatalyst was neutralized by the addition of a strong acid. The isolatedproduct amounted to 1392.2 g. of a light yellow liquid which tended tosolidify on standing at room temperature. This product(t-dodecylamineethyleneoxide had a neutral equivalent of 855.5 which wasequivalent to t-dodecylamine combined with 15 mols. of ethylene oxide.

EXAMPLE 4 In a suitable reaction vessel, there were combined 213.5 g.(0.25 mol.) t-alkylaminopolyoxyethyiene (from Example 3 above) with 62.5g. (0.625 mol.) 98% sulfuric acid, at a temperature of 60 -65 C. over a2-hour period. At the end of this time, there was mixed with thisreaction mixture 51 g. (1.27 mols.) NaOI-I dissolved in 600 cc. ofwater. After separation of the excess sodium sulfate the product (237 g.of t-alkylamino-polyxyethylene sulfate) was isolated as a pale amber,viscous liquid (viscosity 5,120 cps). Analysis of this product gaveresults indicating that the material was 77.0% sulfated.

This product was soluble in boiling sodium hydroxide and soluble up to62 in 7% sodium hydroxide.

EXAMPLE 5 This preparation was carried out exactly as in Example 4 using449.6 g. t-alkylarnino-polyoxyethylene (0.5 mol.) 138 g. (1.375 mols.)97.6% H 89 and 90 g. (2.25 mols.) NaOi-i dissolved in 475 g. water. Theyield of the product (t-alkylamino-polyoxyethylene sulfate), a paleamber viscous liquid, was 475 g. (viscosity=5,860 cps). Analysis of thisproduct indicated that it Was 85% sulfated.

This product was soluble in boiling 5% NaOH and soluble up to 75 C. in7% aqueous NaOH.

It will be apparent to anyone skilled in the alkaline cleaner art thatcertain variations from the compositions and methods set forth above byway of illustration are readily feasible without departing from thescope of the present invention. For example, any of the sulfatedpoiyoxyalkylated tert.-carbinamines described in our previouslymentioned copending application will certainly be suitable. Further,although the specific examples described a typical alkaline cleaningcomposition made with sodium hydroxide, other alkalies of high pH may beemployed. Nor must the percentages of the alkali and surfactant belimited to the 5 percent and 0.07 percent, respectively, that wereemployed by way of illustration in the examples. The surfactant which isthe subject of the present invention is readily soluble in lower orhigher concentrations of alkali and will, within the stipulated rangesof ethylene oxide content and degree of sulfation, perform withcomparable efiiciency in the cleaning of metal and other surfaces.Moreover, the amounts of surfactant may be varied with a proportionateeffect on cleaning etiiciency. Still other modifications are possible,all obviously within the scope of the following claims.

We claim:

1. A surfactant composition consisting essentially of a mixture of atleast one sulfated and one unsulfated tcarbinamine polyoxyethylenecompounds, the unsulfated compounds having the Formula I R2t NH OiHio)mH and the sulfated compounds having the Formula 11 R1 RPNH(C2H4O)m Kin which formulas R R and R are alkyl groups having a total of 11 to 14carbon atoms, In is a value of from 12.5 to 17.5, and X is a monovalentcation from the class consisting of hydrogen and the alkali metals, theamounts of the respective compounds in the mixture being from about toabout percent of the sulfated compound and from about 25 to about 15percent of the unsulfated compound.

2. The composition of claim 1 in which X is sodium. 3. The compositionof claim 1 in which X is hydrogen. 4. The composition of claim 1 inwhich X is potas- Slllfi'l.

References tilted in the file of this patent UNITED STATES PATENTS1,970,578 Schoeller et al Aug. 21, 1934 2,746,932 Vitale May 22, 19562,755,296 Kirkpatrick July 17, 1956 2,768,956 Scott Oct. 30, 19562,871,266 Riley Jan. 27, 1959

1. A SURFACTANT COMPOSITION CONSISTING ESSENTIALLY OF A MIXTURE OF ATLEAST ONE SULFATED AND ONE UNSULFATED TCARBINAMINE POLYOXYETHYLENECOMPOUNDS, THE UNSULFATED COMPOUNDS HAVING THE FORMULA I